NAME

LIBRARY

SYNOPSIS

DESCRIPTION

The profil() system call enables or disables program counter profiling of
the current process. If profiling is enabled, then at every profiling
clock tick, the kernel updates an appropriate count in the samples
buffer. The frequency of the profiling clock is recorded in the header
in the profiling output file.
The buffer samples contains size bytes and is divided into a series of
16-bit bins. Each bin counts the number of times the program counter was
in a particular address range in the process when a profiling clock tick
occurred while profiling was enabled. For a given program counter
address, the number of the corresponding bin is given by the relation:
[(pc - offset) / 2] * scale / 65536
The offset argument is the lowest address at which the kernel takes
program counter samples. The scale argument ranges from 1 to 65536 and
can be used to change the span of the bins. A scale of 65536 maps each
bin to 2 bytes of address range; a scale of 32768 gives 4 bytes, 16384
gives 8 bytes and so on. Intermediate values provide approximate
intermediate ranges. A scale value of 0 disables profiling.

RETURNVALUES

The profil() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.